Many of the ecologically and economically important insect pests are social or subsocial, such as termites, ants and cockroaches. They live in groups and colonies and engage in social interactions, such as mutual grooming and food sharing. Reproduction in a social insect colony is the responsibility of specialized individuals, the reproductives. To eliminate an entire colony, it is necessary to kill not only the foraging population but also the reproductives. An insect colony can occupy a very large area and have a considerable number of foragers (millions), and the location of the nest containing the reproductives is usually difficult to pinpoint, particularly in the case of subterranean termites and ants. Therefore, control of social insects by eliminating entire colonies is challenging. Control of such pests is of economic significance throughout the world. In the United States, for example, the cost of damage and control due to the Formosan subterranean termite (Coptotermes formosanus Shiraki, Isoptera: Rhinotermitidae), a serious invasive pest species found in southeast United States and Hawaii, is estimated at $1 billion annually.
Chemical control methods are associated with certain risks and shortcomings. After the ban of certain soil insecticides (chlordane and other cyclodienes), public demand for reduced-risk, environmentally friendly techniques for pest control has increased. One of the most promising reduced-risk approaches to social insect control that has recently emerged is the targeted bait approach using slow-acting toxicants, such as insect growth regulators (Su et al., “A Review of Subterranean Termite Control Practices and Prospects for Integrated Pest Management Programmes,” Integr. Pest. Management Rev. 3:1-13 (1998)). In baiting stations, foragers consume the bait toxicant. Suppression of a colony depends on the transmission of the active ingredient through the colony via food exchange and grooming among nest mates. A limitation of current baiting schemes is that a large number of foragers must directly contact the bait to spread it throughout a colony. This is because the concentration of bait toxicant is diluted as it is passed from one individual to another during social interactions, until such small amounts are passed that they are not effective against the recipient.
Theoretically, baiting systems could be improved by employing self-sustaining, self-replicating and self-perpetuating biological control agents, such as nematodes, viruses, fungi, and bacteria. Although there is evidence that some of these entomopathogens have effects on insects in lab studies, they have failed to meet expectations in field trials (Culliney et al., “Prospects of the Biological Control of Subterranean Termites (Isoptera: Rhinotermitidae), with Special Reference to Coptotermes formosanus.” Bull. Ent. Res. 90:9-21 (2000)). Their successful use as biocontrol agents is limited due to biological constraints and logistical problems when dealing with social insects. For example, the potency of most pathogens is too weak in their natural state, and they are not generally persistent in the environment. In addition, the target insects are able to recognize and avoid contact with pathogens (Grace, J. K, “Microbial Termite Control,” in Hawaii Agriculture: Positioning for Growth,” CTAHR Proceedings, University of Hawaii, pp. 166-167 (1995)), remove them from their nestmates through grooming behavior, and isolate infected individuals from the colony (Lai, P.Y., “Biology and Ecology of the Formosan Subterranean Termite, Coptotermes formosanus, and Its Susceptibility to the Entomogenous Fungi, Beauveria bassiana and Metarrhizium [sic] anisopliae,” Ph. D. Diss., University of Hawaii, 140 pp. (1977)). Insects also have an efficient immune system for dealing with infections of foreign pathogenic microbes. Therefore, delivery of the pathogen throughout an entire colony would require a large number of initially inoculated individuals and a high dose of inoculum, just as with a chemical bait. This is difficult to achieve when dealing with insects that are not easily accessible, such as ants and termites that live in the soil. Thus, with these foreign pathogens, the level of mass production and re-applications that are required to affect insect groups is expensive, time and labor intensive, not justified by the poor performance, limited to the immediate area of application, and has only a temporary effect (Culliney et al., “Prospects of the Biological Control of Subterranean Termites (Isoptera: Rhinotermitidae), with Special Reference to Coptotermes formosanus.” Bull. Ent. Res. 90:9-21 (2000); and Grace, J. K., “Biological Control Strategies for Suppression of Termites,” J. Agric. Entomol. 14:281-289 (1997)).
The present invention is directed to overcoming these and other deficiencies in the art.